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LTO Battery question
(07-19-2018, 11:18 PM)completelycharged Wrote: My pack is 28kWh (one pack spare until I add nother to make it 32kWh total) and will use 90% range because using a more narrow range with LTO might mean 50,000 cycles but I won't live that long... unless the cells are at a high temperature. One thing to consider if your climate is 30C+ is that the cells have a very low internal reisstance so will give of very little heat when cycling them so putting them in a chilled space will extend the life far more than reducing the cycle range....

Forget the generator completely, if the majority of your use is AC, buy a couple of freezers, fill them with water bottles and then run them 24x7 when you have power and use the bottles (or glycol coollant loop through the freezer) for cooling on the days where solar is not making enough. Ice will store the electrical equivalent of around 100kWh per cubic meter and is far, far cheaper than batteries for cold storage... and can be a lot quicker to extract. Extremerly cheap option is just to take a bottle out and stand it in a tray to capture the condensation. Over time the bottle will thaw while it chills the room. Very unconventional but I think batteries are a bit of a waste for AC and deffinately not for space heating, but that is my view and distorted by the climate and setup in the UK.

The use of a freezer / cold store would allow the pack size to decrease by half or more. Plus, consider than during the times the sun is out and the heat is being generated, so is your power so the AC demand when the sun is shining and being produced will go directly into the AC system and not the batteries so you may end up with only 60% going into the batteries and 40% into the AC, depending on latitude/sunrise/sunset times, etc.

As a suggestion, consider the case of using a lot smaller LTO pack size and implementing a freezer/glycol loop.
These are using the approach for cooling homebrew rather than storing cold.... same implementation and you just run the glycol through when you need the cool boost..

Then again, forget the lot and just implement the homebrew..

Oh, WOW!

I suddenly have a bunch of reading to do, This chilled glycol loop idea is not something I had ever thought of

As far as climate, Texas gets pretty hot, today it was 115F or 46C, It's not always this bad, but summers are generally over 100F or 38C so I plan to keep the batteries inside the climate protection of the cabin, I have read heat makes batteries degrade much faster, so keeping them inside a cabin at 74F or 23C should help slow down the degradation compared to outside storage. This is one more reason I like LTO, they are said to be much safer indoors. 

Hmmmmm, so a heavily insulated chilled thermal mass, this requires some reading, our summers can be pretty warm  Smile 

Thanks again

Indecently the LTO cells they are claiming to have are listed as the 66160H 40Ah, So that's a tiny bit promising 

I've attached the spec sheet they sent me


Attached Files
.pdf   Kylin+power+LTO+2.3V+40Ah+Cell.pdf (Size: 593.46 KB / Downloads: 147)
(07-20-2018, 12:49 AM)completelycharged Wrote: Model "RACEPOW-LTO-66160H" - who or what is RACEPOW...

Cell pictures are standard from YinLong website

This may be closer to the actual cells delivered... depending on source and quality.

Notice on this cell test the capacity is just under 40Ah... and that is still at 1C... not bad for a used cell. This is closer to what is more likely to turn up...

If I can get cells that test out at 40Ah for $14.90 a cell, I'll consider that a big win, Even if shipping and import fees cost me $2000 for 500 cells, my total cost would be $205 a kWh for the cells to make a 46kWh pack and I'd have a 10+ year life out of it, that's gotta be way more cost effective than 18650's and more than 2X as efficient as lead acid

Also not much more expensive than FLA batteries that are going to cost me around $170 kWh, I'd stay away from golf cart batteries and use FLA Rolls Surrette batteries if I was going to go the FLA route, Rolls should also last 10 years, but I desperately want to avoid all the downsides of FLA batteries, they have horrible charge efficiencies especially at the top of the battery, they have so many downsides. 

Also to consider, once I de-rate the FLA battery pack by 50% it becomes more expensive than the LTO cells. FLA batteries are never supposed to drop below 50%, the LTO cells are actually cheaper per usable kWh because I only plan to de-rate them by 80%
First a quick update

The initial quote I received was not to my door, it was a FOB quote, I guess their was some confusion on what I was asking them

Also after making my sample order they reduced their quoted price to $14/cell for 400 batteries

I received some of the pictures I asked for and they answered all of my questions, but now I'm a little more concerned.

When I asked about the batteries history I was told they are brand new

I asked them to clarify, saying surly this is a mistake, that these must be high quality reclaimed cells that have been tested, no?

Their reply was no, these cells are brand new. But everything I read says these will be reclaimed cells, which I'm totally fine with as long as they are tested for remaining capacity, so I don't understand their need to claim that the cells are new

If I buy these cells I'll insist upon a capacity guarantee in the contract stating that the cells will be tested upon arrival and that they guarantee every cell will still have 40Ah of capacity, if they screw me over I can get a refund from my credit card company for breach of contract

I'm really thinking about going a bit smaller, and instead of 500 batteries just using 400 for roughly 37kWh which will be around 30 kWh usable after I de-rate the pack

Total quoted cost for the batteries FOB is $6000 or $162 kWh, I still need to figure out the cost for a freight forwarder to complete the importation, I'm looking at an LTC shipment of  500 KG consisting of 27 boxes each 200*300*400 in size.

Even if this cost is $2000 my total cost per kWh will only be $216, and LTO cells should have a cycle life 10X that of NCR18650B cells, even if it's only 2X, these LTO cells will be more economical over time than 18650's and much easier to construct battery packs with

So if the cell testing goes well I'm going to go with these LTO for my Powerwall

I'll post more updates after I get the sample batteries in, but I'm really concerned with their claim that these are all brand new, I'll have to address this concern in the purchase contract

In case anyone else is interested in the supplier that I'm talking to, their info can be found here

Any recommendations on the best way to test these cells would be appreciated 

(07-19-2018, 10:47 PM)Tim Dale Wrote: So the plan is a Solar array and a Powerwall, I was able to buy a lot of Jinko 325 watt solar panels for $75/ea ($0.23/Watt), I'll put up an 8kW array, this will make way more power than I need, PVWatts shows it should make about 12,000 kW a year

May i ask where you got these as i am in need of a few more panels.. Im in north louisiana
I try... Sometimes i fail.... ok most times. lol
(07-21-2018, 07:38 PM)masteryodajames Wrote:
(07-19-2018, 10:47 PM)Tim Dale Wrote: So the plan is a Solar array and a Powerwall, I was able to buy a lot of Jinko 325 watt solar panels for $75/ea ($0.23/Watt), I'll put up an 8kW array, this will make way more power than I need, PVWatts shows it should make about 12,000 kW a year

May i ask where you got these as i am in need of a few more panels.. Im in north louisiana

There was a guy selling them on Craigslist in Odessa Tx. I'll PM you his #
(07-21-2018, 10:05 PM)completelycharged Wrote: Interesting, especially why they try and sell them as new with images that prove they are not...

Cell + FOB pricing is what I would expect, beware of the FOB shipping sting....

Questions / points would be :
1. ICAO/IATA regulations limit the State of Charge (SOC) to 30% - 2.3V reading on the cell is over 60% SOC, would any manufacturer ship new cells at >60% SOC ?
2. Internal impediance in the spec sheet they sent and the official spaec sheet is sub 1mOhm, thier reading is 1.4 and 1.33mOhms... >30% above spec for "new" cells
3. Packaging with no cell holders, nice.... 20kg of cells in a carboard box with 5mm of packing.

Point 2 is the very reason they are "recycled" - try fast charging them at 10C at a bus stop.... 400A x  1.4 mOhm = 220W heat dissipation while charging.. from one cell !!!! Put another way 24% of the charge energy is lost as heat.... (400^2 x 0.0014) / (400A x 2.3V = 920 Watts) this is the impact of IR.... and why they are recycled...

Use them in a powerwall at 5A 0.28% heat loss.. no real issue. 40A, 2.3%, 80A 4.5%. 200A 11.3%.

From the images there are a few things, which raise issues for me, so beware.

I would need a lot lot more proof before sending them $x,000 before they release the goods... no seller will put them on a boat without full payment...

Max I'd ever be pushing or pulling from the pack would be when charging on a perfect day with the 7.8 KW array I'm going to be putting up, and it will never be that high in reality, on a perfect day (24) 235 watt solar panels will probably max out around 7KW (Just a guess)

I think my intended use will be pretty easy on a 36kWh 396 cell 22S18P 48V pack 

The seller said they do guarantee every cell will load test 40Ah, they have clearly communicated this fact and they are now pretty much bound to it legally if there is a future dispute. I think their claim is BS, but I'm also no expert, just a random internet guy trying to build a diy powerwall to save come money Smile 

Is there a way to use the IR reading to tell how much life these cells would have in my specific application, estimate the Ah capacity left in them? 

If I pay with my credit card I get purchase protection from fraud, as long as it's under $10,000, and this certainly will be. If the seller misrepresents what they are selling I can dispute the charges after I get the batteries and have them tested for capacity , I'll clear and confirm that with my credit card company before making the purchase 

By the way, do you know if your supplier still has these batteries for sale and if they are a similar cost? 

Thanks again for you help

Good luck with the credit card.

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